1. Field of the Invention
This invention relates generally to level gauge or measuring apparatus and, more particularly, is directed to a level gauge apparatus suitable to detect or gauge the liquid level or the level of the interface between different kinds of liquids such as water, oil and so on, for example, within a tank.
2. Description of the Prior Art
FIG. 1 is a partially exploded perspective view illustrating a construction of a known level gauge apparatus. Referring to FIG. 1, an example of the prior art level gauge apparatus will be described hereinafter.
As shown in FIG. 1, there is provided a float or displacer 1 that is movably suspended by a wire 2 so as to float on the surface of a liquid or the liquid level (not shown). This wire 2 is wound around a wire drum 3 and can be supplied therefrom and/or rewound therearound. The wire drum 3 is rotatably supported at its bottom 3a by a detection shaft 8. When the liquid level on which the displacer 1 is floated is changed and hence the displacer 1 is moved up and down in response to the change of the liquid level, the tension applied from the wire 2 to the wire drum 3 is changed. This change of tension given by the wire 2 is converted through a coupling outer magnet ring 4 fixed at its one end to the bottom 3a of the wire drum 3 being coaxial with respect to the shaft 8 and a coupling inner magnet ring 5 fixed at its center to the shaft 8 within the ring-shaped magnet 4, to the torque of the detection shaft 8. This torque of the detection shaft 8 displaces through a metal member 9 that is fixed to the detection shaft 8 balance springs 11 one ends of which are fixed to the metal member 9, respectively. While, the metal member 9 and the balance springs 11 are shown to be distant apart from a worm wheel 13 which is rotatably supported by the detection shaft 8 in FIG. 1 for better understanding, the metal member 9 is fixed to one side surface of the worm wheel 13 and the other ends of the balance springs 11 are fixed through L-shaped metal members 12 to the same surface of the worm wheel 13, in practice.
The displacement of the balance springs 11 is converted to an electrical signal by a magnet 10 fixed to the metal member 9 and an electromagnetic transducer 14 attached to the surface of the worm wheel 13 at the position corresponding to the magnet 10. The electrical signal from the electromagnetic transducer 14 is transmitted through a slip ring 16 fixed to the detection shaft 8 to a servo amplifier 17 and thereby amplified. The electrical signal amplified thereby is supplied to a motor 18 and its rotation or drive shaft 19 rotates through a worm 20 which is formed on the outer surface of the drive shaft 19, the worm wheel 13 which meshes with the worm 20 in the positive or reverse direction in response to the displacement of the liquid level. When the liquid level for the displacer 1 is not displaced any more, they stop rotating, the equilibrium state then being kept. While, the rotation of the drive shaft 19 operates a level gauge counter 22 through a belt 21 and thereby the value of the liquid level gauged can be displayed on the level gauge counter 22 when the displacer 1 is settled. There are provided a pair of bearings 6 and 7 that are used to support the detection shaft 8 rotatably. Further, there is provided a ball bearing 15 to allow the detection shaft 8 and the worm wheel 13 to be rotated freely and reciprocally.
By the way, the above mentioned known level gauge apparatus must be constructed such that the detection shaft 8 and the worm wheel 13 can be freely rotated by using the ball bearing 15 or the like. Inevitably, this makes the known level gauge apparatus become complicated in construction and high in cost. Further, due to the mechanical friction generated among the detection shaft 8 and the bearings 6 and 7 for supporting the detection shaft 8 and the mechanical friction generated among the detection shaft 8, the ball bearing 15 and the worm wheel 13, the known level gauge apparatus is degraded in mechanical detection sensitivity to detect that the tension applied to the wire drum 3 by the wire 2 is changed when the liquid level is displaced. For this reason, the prior art level gauge apparatus can not increase its mechanical detection sensitivity. Further, the prior art level gauge apparatus can not effectively utilize the most-advanced servo amplifier which is highly stable and high in amplification factor. Thus, it can not be expected that the known level gauge apparatus will be enhanced more in mechanical detection sensitivity.